Steam generator



Oct. 30, 1962 R. CUNNINGHAM, JR., ETAL 3,060,905

STEAMGENERATOR Filed Sept. 24, 1957 6 Sheets-Sheet l lllllll lNVENTORS RlCHARD CUNMNGHM JR.

, HORACE R. RXX

ATTY.

Oct. 30, 1962 R. CUNNINGHAM, JR., ETAL 3,060,905

STEAM GENERATOR 6 Sheets-Sheet 2 Filed Sept. 24, 1957 m; N: m2

f NV ENTORS MCH/XRD CUNNNGHM JR.

NOR me R. Rm

Oct. 30, 1962 Filed Sept. 24, 195'? R. CUNNINGHAM, JR., ET'AL. 3,060,905

STEAM GENERATOR 6 Sheets-Sheet 5 HOR ACE R. RM1

ATT Y.

0d 30, 1962 R. CUNNINGHAM, JR., ETAL. 31,060,905?

STEAM GENERATOR 6 Sheets-Sheet 4 Filed Sept. 24. 19577 7l Y- me,

lOl

Q9 fig. 6

ATTY.

Oct. 30, 1962 R. CUNNINGHAM, JR.; ETAL 3,060,905

STEAM GENERATOR Filed sept. 24, 1957 e sheets-sheet s I 99. il

NVEMTORS RCHRD CUNNNGHAM JQ.

HORACE R. RD(

BY//wwy 4h.

TTY. l

Oct. 30, 1962- R. CUNNINGHAM, JR., ETAL 3,060,905

STEAM GENERATOR Filed sept. 24, 1957 e sheets-sheet e INV ENT ORS HCl-IARD CUNNINGHAM JQ,

HORACE R. QM

ilnited dtates 3,060,905 STEAM GENERATR Richard Cunningham, Jr., and Horace R. Rix, Houston, Tex., assignors to Vapor Heating Corporation, Chicago, Ill., a corporation of Delaware Fired sept. 24, 1957, ser. No. sesam S Claims. (Cl. 122-448) This invention relates to steam generators of the water tube class wherein the water to be converted into steam is forced in a continuous stream through one or more heating coils.

In the above class of generators, as heretofore constructed, a portion of the water is converted into steam within the heating coils and is discharged therefrom as a mixture of steam and hot water into a steam separator wherein the Water separates from the steam by gravity, while the steam is discharged lfrom the separator through a main steam pipe. Such generators have not been entirely satisfactory, since the generation of steam takes place within the coils and therefore requires the coils to be maintained at high temperatures. These high temperatures cause rapid deterioration of the coils and therefore result in high maintenance cost in connection with the repair and the replacement of the overheated coils. The said generators usually include some provision for reclaiming a portion of the heat contained in the hot water separated from the steam, but these provisions have been inadequate to effect substantial economies, since the volume of hot Water returned to the generator as makeup Water is usually quite small in relation to the volume of unheated water pumped into the heating coils. Consequently, the feed water, as a whole, is preheated within the coils of the generator.

One of the principal objects of the present invention is to provide a steam generator of the above general class which is constructed to operate on a principle which avoids the above mentioned and other objectionable features embodied in water coil steam generators as heretofore constructed. In this connection, our improved generator is so constructed that a substantial pressure drop exists between the pressure maintained in the water heating coils and the pressure maintained in the steam separating chamber, whereby a portion of the high temperature water discharged from the high pressure of the heating coils into the lower pressure of the steam separating chamber will flash into steam within the separating chamber. The other portion of the water falls by gravity to the lower portion of the separating chamber wherein it receives additional heat by virture of its direct contact with the walls of the heating chamber and is thereafter recirculated through the water heating coils.

Another object is to provide a structure which will maintain the water at high temperatures, but which may be so operated as to avoid overheating of the coils. In this connection the heating chamber is arranged within the steam separating chamber so that the water separated from the steam, together with additional feed Water delivered into the separating chamber, completely surrounds the heating chamber casing, it being by this arrangement that additional heat is added to the water within the separating chamber. A quantity of this water, in excess of that which is necessary to safeguard the coil structure from destruction by overheating is circulated through the heating coils. The volume of water thus circulated through the coils is approximately three or four times that which is necessary to prevent said overheating. The large body of water thus maintained in the steam separating chamber eliminates the need for minutely controlling the water delivered to the heating coils during variations in the volume of steam produced. The high volume of water pumped through said coils also functions to stabilize the operation of the generator by preventing pressure surging effects Within the generator during abrupt chan-ges in the demand for steam.

Another object is to provide the improved generator with compact and simplified construction which presents heat transfer surfaces adapted to be wiped by hot gases of combustion, which surfaces are larger than those of other generator constructions of equal size. The compactness of the generator assembly makes it highly suitable for use in situations where conservation of space is an important consideration.

A further important object is to provide novel constructions in a -steam generator of the water coil type which makes -for ease in the initial assembly of the coils and for removal and replacement thereof. It is also the aim of the invention to provide improved constructions which make it practical to produce a generator assembly having a single heating unit of predetermined capacity or to vary the construction to include a multiple of such heating units when generators of larger capacities are desired.

The above mentioned and other incidental objects of the invention are attained by the novel constructions and arrangements illustrated herein including the provision of a water heating unit comprising one or more tubular coils which are so constructed and arranged within a heating chamber shell that hot combustion gases delivered into the heating chamber will wipe substantially the entire area of the heating coils and also the entire area of the inner surface of the heating chamber shell. The said Shell is positioned within an outer casing which functions as a steam separating drum and hot water collector. A spray head is located in the upper portion of the steam separating drum and receives hot Water discharged from the heating coils. The spray head is provided with a series of apertures from which the hot water is sprayed under high pressure into the steam separating drum wherein a considerably lower pressure is maintained. As a result of this pressure diiferential a portion of the water discharged from the sprayhead ashes into steam. The steam passes upwardly through a mist collector to an outlet pipe, while the other portion of the hot water drops by gravity into the lower portion of the said drum wherein a body of such collected Water, together with additional feed water added thereto, surrounds the heating chamber shell as previously indicated and receives heat therefrom by virtue of its direct contact with the outer surface of the hea-ting chamber shell.

The entire assembly thus briey described is supported on a skid structure which also serves as asuitable` mounting for the water feeding and circulating pumps and for a blower for supplying combustion air to the tire chamber. The feed Water pump is controlled by a oat actuated control means which functions to maintain a predetermined water level in the steam separating drum 11.

The invention is illustrated in certain preferred embodiments in the accompanying drawings wherein:

FIG. l. is a side view of one form of steam generator having a single heating'unit and showing certain parts thereof in section-and other parts in elevation;

FIG. 2 is a rear view in elevation of the assembly shown in FIG. 1;

FIG. 3 is a front View in elevation of the structure shown in FIG. 1; f

FIG. 4 is a horizontal sectional view of the generator shown in FIG. 1 with the intermediate portion thereof broken away to better illustrate the location of a water circulating pump and its connections to the inlet ends of the water heating coils;

FIG. 5 is a cross section taken on line 5 5' 'of FIG. l;

FIG; 6 isa sectionalview of a pressure motor and fuel valve operated by said motor;

FIG. 7 is a front view in elevation of a steam generator composed of a plurality of water heating units corresponding to the units shown in FIG. l; and

FIG; 8 is a4 rear view` in elevation of the embodiment shown in FIG. 7.

Referring tirst. to FIGS. 1 to 6 inclusive, wherein'A a steam generator assembly therein shown includes a single' water heating unit: This' embodiment of the invention comprises awater heating unit including a heating charn-l ber` shell 10 positioned to extend into an outer casing 11 which is closed with front and rear end walls 12 and 13 and functions as af steam separating drum andV hot water collector. The front end wall 12 of the outer casing 11 is preferably` formed with a flat face and'is reinforced by a series of stay bolts 12a located at. spaced location to prevent bulging of the end wall'when it is subjected to internal pressure. The said drumlis supported on a skid 14 comprising a rectangular base composed of side and end Vsills 15 and 1.6 suitably welded together as indicated at 17, 118. A bottom panel 19 is welded asindicated at 20 to the side and end sills of the skid. Four supporting posts 21, preferably in the form of vertically extending channels, are securely welded to the base portion of the skid, the upper ends of the post 21 being welded as indicated at 22 to the opposite sides of the steam separating drum 11 near the forward and'rear ends thereof.

A spray head 2,3l is supported in the upper portion of the drum 11 by means of a series of metal straps 24 attached to a frame work Z'Slwelded to the upper portion of the drum' 11V as indicated at 26. The said frame work 25 also serves to support a body of wire mesh 27 which functions to collect the mist held in suspension in the steamA as the latter passes throughv the mist collector to a steam outlet pipe 28; ThisV pipe is welded as at 29 inan opening formed in the top-portion ofY the drum 11.

Water H eating. Unit Thei shell: 1b of. the water heating unitisclosed at its rear. endbya 'wall.29 and open at itsforward end. This endts into an opening 30 formed. in the forward end wall 12 ofthe steam separator drum 11 and is sealed therein by a. weld 31. The rear wall 29 of the shell is formed with. a pair of circular openingsA 32-33 which arealignedy with ai similar pair of openings 341 and 35 formed in the rear wall 13 of said drum. A pair of short pipesections. 36,` 37V are fitted into the opposing openings 32,'34vand 33, 3S, respectively,` and areweldcd therein to bridge: the space` 38 between the rem wall 29 ofthe heating chamber.v shell 10` and the rear wall 13 of the drum 11 and cooperatewith. the welded connection of. the forward end of Vtheshellto the front. wall of the drum to support the.y shell inv a. iixedthorizontali position within the drum.

Water H eating C'ols A pair: ofA concentricallyarranged. watery heating coils 39, 40 are positioned within the heating chamber shell 10. The tail ends 41 and 42' of the said coils extend through; thev bridge conduits 36 and? 37 and are. clamped therein by sealing plugs 43, 44. The inlet ends 45 and v46respectively, ofithe said coilsy arefconnected. in parallel withthe outlet port 52 of a circulating pump. 47 by means of piping 48 and 49 leading'to a T-iitting 50 and thence by a pipe section 51 to the.- said outlet. port 5270i the pump 47. The inlet port 53 of the circulating pump is onnectedby piping 54 communicating with the interior of the steam separating drum 11 at a location 55 (see FIG. l), positioned a suitablecdistance above the bottom of the drum so that water withdrawn from the drum,v as hereinafter described, for recirculatiug through the coils 39,Y 40 will be free of scale and/or mineral sludge which may collect in the bottom ofthe drum.

The inner coil 39 includes a series of contiguous convolutions or turns' 56 which-define a heating chamber i 57, the forward end of which communicates with a tire pot 5S, hereinafter described, which delivers hot combustion gases into the heatingL chamber to heat the water contained in the coils and to also apply heat to the side and end walls of the heating chamber shell 10. When the inner coil 39 is in its operative position, it is spaced from the cylindrical side wall of the heating chamberA shell 10 so as to define an annular space 59. rlEhe rear end of the coil 39 is provided with spaced. apartV convolutions 60, 61 to provide lateral passageways 62 through which hot gases of combustion may pass from the heating chamber 57 into said annular space 59. The rear end of the Vinner coil 39 also stops short of the rear end wall 29 of theheating chamber shell and, consequently, provides an additional passageway 63 into the concentric space 59, whereby the hot gases which impinge against the end walll 29 of the shell 10 will tind entrance. into the said annular space 59. These gases will pass through said space to a smoke box chamber 64 and to a smoke stack 65, the latter being supported on the smoke box chamber` housing 66. The housing is` removably attached to the front Wall 12 of the drum 11 by means of bolts 67.

The outer coil 40- is positioned within the said concentric space 59 and is formed throughout its length with spaced apart convolutions 68 and 69. The convolutions 63 are wound somewhat larger in diameter than the convolutions 69 and are arranged in close relation to the inner surface of the heatingy chamber shell 1t)` so that the hot gasesof combustion are compelled to follow a circuitous path, as shown by arrows in FIGS. 1 and 4 of the drawings, between the convolutions 68, 69 and thereby wipe substantially the entire area of these convolutions. The said gases also wipe the Vinner surface. of they heating chamber shell 10 andthe undulating outer surface of the inner coil 3g. The. undulating outer and inner surfaces of the inner coil 39-promote turbulence inthe hotgases, whereby the gases are brought intorecurrent wiping contact with the Walls and thereby promote highk thermal eiciencyr Spray Head and" M ist Collector The tail ends 41 and 42 of the coils 39 and 40 are connected by means of piping 70 and '71, respectively (shown best in FIG. 2), to a T-tting 72 leading into the spray head 23. The spray head is formed with a large number of spray openings 73 arranged inV a series` of rows lengthwise thereof (see FIGS. l yand 5). These openings are suiiiciently restricted in diameter to maintain a water pressure within the spray head 23 considerably higher than the steam pressure maintained in the separatingpdrum 11. During normal operations the. pressure in the. coils 39 and 40v will range between 100 and 120 p.s.i. The pressure in the. spray head,v under such condition,v will be approximately 60 p.s.i. and the pressure within the.- sep arating drum will be approximately l5 psi. Consequentfr ly, a portion of the high pressure; hot Water discharged from the spray head 23 into thek lower pressure steam separating chamber willflashiinto steam. The other portion of the water discharged falls into the bottom portion of the drum 11 to assist in forming av large body 74 of water which surrounds the heating chamber shell 10 and is heated by virtue of its direct contact4 with the: outer surface of said shell. Additional water is. added to the said body 74 to maintain it at the level indicated at 75 in FIG. l. This additional Water is drawn from a supply source (not shown.) by means of a feedv pump 76 mounted onthev skid 14 and operated by an electric motor 77 or other suitable. prime mover. The water is delivered into the'drum 11 through the feed pipe 78 and the water level 75 is indicated by a sight glass '79. This level is automatically maintained by a switch mechanism 147 contained in the housing and actuated by a float 81 to control the operation of the feedv pump motor 77l Referring again to the heatngcoils: The inner coil 39, with its closely wound convolutions, provides the'heating land thereby oscillates a gear segment 112a.

chamber 57 of suicient length to burn the heavier oils as a fuel. It is also desirable, since the inner coil 39 has initial contact with the high temperature flame and hot gases, to force a larger volume of water through this coil than is passed through lthe outer coil 40, the latter coil being subjected to less intensive heat. Therefore, a flow restricting device 82 is positioned in the piping 71 leading from the discharge end of the outer coil 4t? to the spray head 23.

Smoke Box Fire Pot and Plenum Chamber n The fire pot 58 is aligned with the tire chamber 57 and 1s supported in this position by virtue of its welded attachment to a re stabilizing ring 33. The said ring is attached by a weld connection S4 to one end of a cylindrical wall S5, which in turn is welded at its other end 86 to the front Wall 87 of the smoke box. rPhe cylindrical 85 cooperates with the cylindrical side wall 66 of the smoke box to define the smoke chamber 64 for receiving the spent products of combustion from the annular passage 59. The said cylindrical wall also cooperates with the cylindrical wall of the tire pot S8 to define a plenum chamber 37a. Combustion air is delivered into the plenum chamber from a blower S8 located beneath the generator, and the air is directed in part, as primary combustion air, through a hooded central opening 89 leading into the iire pot 58, where initial combustion takes place. Additional secondary combustion air is delivered into the re pot 58 through a series of apertures 90 formed in the side wall of the re pot near the fire stabilizing ring 83. The air jets from the said apertures 9@ are directed radially inwardly toward the flame `and therefore promote turbulence and insure complete combustion of the partially ignited gases as they pass into the heating charnber S7.

The plenum chamber 87a has a central opening 91 which is closed by a plate 92 removably secured thereto by bolts 94. A fuel nozzle 93 and a pair of ignition electrodes 95, 95 are secured to the removable plate 92 in a position to project through the hooded opening 39 and into the interior of the fire pot 5S.

Fuel Control Fuel is drawn through a conduit 97 from a fuel reservoir 109 by a pump 9S and is delivered by said pump through conduit 99 to a fuel control valve 160 and thence .through conduit 101 to the fuel nozzle 93. The fuel pump 9S is operatively connected to the shaft 102 of the blower S8 which supplies the combustion air to the plenum chamber 87a. The said blower is driven through belt connections 103 from the same power source, a motor 104, which operates the circulating pump 47. Consequently, the water circulating pump 47, the blower 83 and the fuel pump 98 are all -operated continuously at a -xed rate. When desired, an air compressor 105 (FIG.

.7) may also be operated by the said motor 104 by a suitable belt connection 106.

Inasmuch as the fuel pump 98 is operated continuously and the delivery of fuel to the nozzle 93 is varied by the valve 100, a pressure relief tting 96 is connected in thev fuel delivery line 99 at the pump to minimize back pressure. A conduit 108 leading from the pressure relief fitting 96 returns the surplus fuel from the pump back to the fuel supply reservoir 1%9.

A damper 11) is interposed in an air inlet chamber 111 leading into the blower 88 and is automatically ad- 168 beyond the orifice fitting 113 at T-tting 114. The

pressure of the oil in conduit 107 operates the motor 112 A pinion 112!) secured to the damper shaft is rotated by the gear segment 112a to alter the position of the damper 11-0.

Fuel Valve Motor The position of the fuel valve 10u for varying the delivery of fuel to the nozzle 93 is controlled by a pressure motor 115 which responds to pressure variations within the steam separating drum 11. The pressure motor 115 comprises a casing composed of upper and lower sections 116, 117. A diaphragm 118 separates the casing into upper and lower chambers 119, 120. The upper chamber communicates through a conduit 121 with the interior of the steam separator drum 11 and impresses the pressure therein on the diaphragm 11S. A push rod 122 depends from the diaphragm 11S and extends through an adjustable spring seat 123. A spring 124 seats on the spring seat 123 and exerts pressure against an abutment plate 12S secured to the push rod 122 so as to exert spring pressure in opposition to the fluid pressure in the upper chamber 119. The spring pressure exerted can be adjusted by rotating the spring seat 123. The lower end of the push rod 122 is spaced from the upper end of a stem 126 of the fuel valve which stern projects upwardly from the fuel valve casing. This spaced relationship is maintained between the push rod 122 and valve stem 126 until the pressure within the drum 11 reaches a predetermined value as determined by the adjustment of the seat 123. When the pressure within the said drum exceeds said predetermined value the push rod engages the valve stem 126 and moves the stern and its Valve in a direction to reduce the delivery of fuel to the nozzle 93. Alternatively any reduction in the steam pressure below the selected value, results in movement of the diaphragm, under the force exerted by spring 124 in .a direction to relieve its pressure on the valve element 127 whereupon this element is moved by the force of a spring 128 in a direction to increase the delivery of fuel to the nozzle 93.

Referring again to the smoke box and the purpose of its removable attachment to the steam separating drum 11: The fact that the smoke box is secured to the said drum 11 by means of bolts 67 makes it readily detachable to facilitate insertion of the water heating coils 39 and 40 into the heating chamber shell 10 and also facilitates their removal from said shell. In order to further simplify the insertion and removal of said water coils, the piping leading to the inlet ends 45 and 46 thereof are provided with unions 130 and 131 whereby the water feed piping may be disconnected to facilitate removal and replacement of the coils. In this connection the piping 70' and 71 is provided with similar unions whereby portions of the discharge piping 70, 71 may be disconnected from the water coils per se. The fuel conduits .101 and 107 and the air conduit 132 are also provided with couplings 133, 134 and 135 to facilitate their detachment from the nozzle structure in the event it should be necessary or desirable to remove the nozzle structure. The air pipe 132 supplies compressed air to atomize the fuel. This air may be supplied by the air compressor previously referred to or from any other suitable source.

When it is desired to blow down the steam separator drum to remove any scale or sludge which may have.

collected in the lower portion thereof a blowdownvalve 136 is opened so that the said scale and sludge may be drained through pipe 136a.

Summary of Operation eration of the feed pumpmotor 7-7. After the proper Water level in the drum 11' has been established, the

.motor 104 is set into operation` to operate the fuel pump 98 to deliver fuel to the nozzle 93 and also operate the blower 88 and the water circulating pump 47. The circulating pump 47 withdraws water from the body of water 74, which after the boiler is in operation, has been heated by virtue of` its contact with the heating chamber shellv 10 and forces this water into the heating coils 39 and 40'.V The heated water is delivered from the said coils into the' sprayv head 23 from` which it is dischargedV into the' upper portion of the drum 11. A portion of the water discharged ashes into steam within the said drum, as previously described, and the remaining water falls by gravity into the body of Water 74 for recirculation through the heating coils 39 and 40. A mist collector 27 located in the upper portion of the drum 11 functions toV collect the mist contained in the steam and thereby return this condensate to the said body of water 74 while the steam discharges through the main discharge pipe 28.

When the steam within the said drum 11 rises to a predetermined value, the push rod 122 of the fuel valve motor 115 engages the upper end of the valve stem 126. In the event that the steam pressure Within the drum 11 continues to rise above said predetermined value, the push rod 122 will depress the valve'stem 126 of fuel valve 100 andv thereby reduces the delivery of fuel to the nozzle 93.

The temperature of the Water discharged from the heating. unit may be controlled by means of a pair of temperature responsive switches 137 inserted in the discharge piping 70, 71 leading from the inner and' outer terminals '41, 42 ofthe water' heating coils 39, 46. The said switches 137 may be connected in series so that' either will function to interrupt the operation of the motor 164 and thereby interrupt the operation of the circulating pump 47, blower 88 and fuel pump 9S so as to cut ot the delivery of heat to the heating unit 10. When the temperature of the water recedes to a predetermined low temperature limit, both switches 137 must reclose to activate the motor 104 and thereby re-activate the mechanism for circulating. Water through the coils 39, 4G and' for delivering fueland air to the lire pot 5S. The resultant decrease in the intensity of the heat within the heating chamber 57 is quickly reectedin a decrease of the steam pressure in. the drum 11. In such case the motor diaphragm ofthe valve motor 115 and the push rod 122 will recede toward. their normalpositions and the spring 128 associated with the fuel valve 127 will move the valve in a direction to increase the delivery of fuel to the nozzle93. Thev variation in the delivery of fuel to thenozzle 93 does not result. in the developmentv of! pressure surges within the drum 11, since the large volume ofhot water. circulated through the coils 39 and'lavoids abrupt changes in temperature of the coils so that pressure. changes within the drum 11` are brought about gradually. Y

i Modified Generator Referring-now tothe modicationrshown in FGS. 7 and 8 off the drawings: The modiiied. generator comprises threewater heating units 10a, 10b and lllc constructed as illustrated ina FIG... 1` andenclosed within a single. drum designated 11a. Three smoke boxes, one for each Water heating unit, are designated 66a, 66h and 66o. Each smoke box corresponds in construction to the smoke box 66 shown in FlG. 1, except that they communicate through Separate branch pipes'129a, 129i;y and 129C with a single smoke stack 65a.

Water` Circulation for Modified Generator A water circulating pump 47aA operated byY a'. prime moven. for: example an electric motor 104a, withdraws water from the interior of the. drumv 11a through a pipe 54a and delivers it into a. manifold piping 50a. This manifold is connectedv by branch pipe connections to the inlet ends of the water coils ofieach of the heating units 16a, 1%, we. Branch pipe 43a connects the manifold 50a with the inlet end 45a` of the inner coilf of the heating unit 10a. A branch 48h connectsrthe manifold 50a with the inlet 4512 of the inner coil of the heating coil 1Gb; and branch section 4gb connects the said manifold with the inlet end 45C of the inner coil of heating unit 19C. The inlet end `46a of the outer coil of heating unit 10a is connected to the manifold 56a by branch piping 49a. The inlet end 4Gb of the outer coil of heating unit 10b is connected with the manifold 50a by a branch 4917, and' in unit 19o the inlet end 46c of the outer coil is connected to manifold 50a by a branch 49C. The branch pipes leading to the inlet ends of the coils embodied in each of the heating units are provided with unions 141 and shut oit valves 142 whereby the water coils of any one or more of the heating units 10a, ltlb or 16o may be rendered inoperative or may be removed from the general assembly for the purpose of repair or replacement Without affecting the operation of the other heating units. The removal of such coils may be accomplished by removing the associated smoke box 66a, blib, or 66e in the same manner as described in connection with FIGS. l to 4, inclusive.

Referring nowV to FlG. 8: The outlet ends of the coils associated with heating units 10a, 10b and 10c are connected in parallel with a spray head 23a by pairs of branch piping 70a, 71a; 70h, 7lb; and 70e and 71C. The water thus delivered to the spray head 23a is sprayed into the drum 11a`in the same manner and with thev same results as described in connection with FIG. 1. Each paire-fV said branches 70a, 71a; 70b, '71b; and' 76o, '71o have couplings 143 and shut off valves 144 therein to facilitate ready removal of the coils associated with any one or more of the water heating units 16a, 1Gb, 10c. IdenticalV flow restricting iittings 82o, 82h, 82C are interposed in the pipesA 71a, 71b anlcl'71c so that the greater volume of water will flow through the innermost coil of the several heating units lila, 10b and ltc.

Feed Wafer Pump Control Additional ymake-upV water is delivered into the drum 11a by means of a feed water pump 76a. Said additional Water is drawn from a source (not shown) through a pipe 146 and is delivered into the drum 11a through pipe 78a. The water level 75a is maintained substantially constant withinv the drum 11a by means of a switch mechanism 147er within the housing 80a, the Switch being controlled by a iloaty 81a. Said switch mechanism 147a controls the operation of thefeed pump motor 77a so that the feed pump 76a may be activated and deactivated, as may be required, to maintainthe water level a substantially constant. A sight glass 79a indicates the water level 75a for the purpose of visual inspection.

Fuel Control for Modified Generator FuelA is delivered to. the several4 nonle assemblies 93a, 31: and 93o from a single. fuel pump 98a which is operatively connected to the shaft` 10211 of a. blower 88a, the blower being operated by motor Ilma. which also operates. thecirculating pump 47a. The fuel pump 98a draws fuel oil from a reservoir 109a through conduit a and delivers it through conduit 99a to a control valve lltla, and thence into a manifold conduit lilla. The manifold conduit 101e communicates through branches 148, 149 and 15) to the nozzle assemblies 93a, 9312 and 93e, respectively. The said branches are detachably connected to said nozzle assemblies by connectors 151, 152 and 153. 'Ihey are also provided with shut-olf valves 154,V whereby theY fuel supply to any one or more of the nozzle assemblies 93a, 93h or 93C may be shut oit inv the` event. thatV a nozzle assembly is. to be. withdrawn from inspection. on repair or in the' event that it. is desired to remove one or more of the smoke boxes 66a, 66h or 66C to permit the withdrawal of the Water heating coils from one or more of the heating units a, 10b, 10c. The said fuel control valve 100a and its pressure operated motor 115a are the same in construction and operation as shown and described in connection with FIG. 5. Full pressure in the manifold conduit 101a is impressed on the pressure motor 160 by means of the branch conduit 107a. Pressure motor 160 adjusts the damper 110a so as to vary the delivery of combustion air to the several heating units 10a, 10b and 10c in relation to the fuel pressure delivered to the nozzles in the same manner as described above for the single heating unit. The said air is delivered from the blower 88a into a trunk line 156 connected by means of branches 157 and 158 and 159 to the plenum chambers associated with the several heating units 10a, 10b and 10c.

Compressed air for atomizing the fuel is supplied from a suitable source, for example a compressor 105 operated by the motor 10451. The compressed air is delivered by the compressor 105 into a manifold supply conduit 161 which is connected by branches 132:1, 132b and 132C to the several nozzle assemblies 93a, 93h and 93C.

The temperature of the Water discharged from the heating units 10a, 10b and 10c may be controlled by means of temperature responsive switches 137a inserted in the discharge piping 70a, 71a, 70b, 71h, and 70e, 71e leading from the inner and outer terminals 41a, 42a, 41b, 42b, and 41e, 42C of the Water heating coils. The said switches may be connected in series lso .that the opening of any one of the switches at a predetermined temperature will interrupt the operation of the motor 10411 and thereby interrupt the operation of 4the circulating pump 47a, blower 88a, fuel pump 98a and air compressor 160. As soon as all of the temperature responsive switches are closed the steam generator will be re-activated.

It will be observed from the above description of the modified generator that the heating coils of any one of the heating units 10a, 1017106 can be readily removed from their associated shell for lrepair and/or replacement without affecting -the operation of the steam generator insofar as the other heating units are concerned. It will also be observed that the heating unit shells 10a, 10b, 10c, being welded to the front wall of the drum 11 and being secured to the rear wall by means of the bridge conduits, cooperate with the stay bolts 12a to reinforce the front end wall to prevent bulging thereof when it is subjected to internal pressure.

We claim:

l. A steam generator comprising a closed external drum for containing a body of water therein, a fuel burning water heating unit including a heating chamber shell sealed in said drum and completely immersed in and consequently cooled by said body of Water, the shell having openings at opposite ends thereof leading to zones externally of the drum, a water heating element insertable into said shell through an opening at one end thereof and having its discharge end projecting through an opening at the other end of the shell and communicating through a spray head with the interior of said drum, a circulating pump for withdrawing water from said body within the drum and forcing it through said heating element and spray head into the said drum at pressures higher than that maintained in the drum whereby a portion of the discharged water flashes into steam within said drum and the remaining portion of the hot water discharged falls into said body of Water, and means for delivering hot gases into said heating chamber shell to apply heat to said body of water and to the water in said water heating element.

2. A steam generator according to claim l characterized in that a steam discharge pipe communicates with the upper portion of said drum and a vapor collector comprising a body of wire netting for collecting mist suspended in the steam is positioned in the said drum intermediate said spray head and said steam discharge PI3. A steam generator according to claim 1 characterized by the provision of means defining -a smoke box positioned to communicate with the heating chamber shell and is removably attached to the forward end of said drum, and unions interposed in the inlet and discharge piping associated with said water tube coils and cooperating with said removable smoke box to facilitate ready removal and replacement of the water tube coils.

4. A steam generator according to claim 1 characterized by the provision of a nozzle for delivering fuel into said lire pot, a fuel control valve positioned Iin the flow path of the fuel -to the nozzle, and means responsive to pressure changes in the generator for proportionately varying the position of said fuel valve to increase the fuel delivery during a decrease in pressure and to decrease the fuel delivery during an increase in steam pressure.

5. A steam generator according to claim 4, provided with means responsive to the temperature of the water discharged from the water heating unit for increasing the circulation of water lthrough said heating unit during a temperature rise and for controlling the operation of the fuel and combustion air delivery means [to decrease the volume of fuel and air delivery.

6. A steam generator according to claim 1 characterized by the provision of a plurality of water heating units positioned in said drum and immersed in the body of water therein.

7. A steam generator according to claim 6 in which separate fuel nozzle assemblies are provided for each heating unit, a fuel pump, a fuel control valve for receiving fuel from said pump, a manifold delivery conduit communicable with said fuel pump, detachable branch conduits leading from the manifold pipe to the several nozzle assemblies, and means responsive to the steam pressure Within the generator for adjusting the position of the fuel valve to increase the fuel delivered during a drop in steam pressure within the generator and to decrease the delivery of fuel during an increase in steam pressure.

8. A steam generator according to claim 1 characterized in that the said Water heating element includes inner and outer concentrically arranged water tube coils positioned in said heating chamber shell in a position to be wiped by the hot gases delivered into said heating chamber shell, means connecting said inner and outer water tube coils in parallel with said circulating pump, and a flow restricting means positioned in the flow path of the water discharged from the outer coil, whereby a larger volume of water is passed through the inner coil than is passed through the outer coil, so as to avoid overheating ofthe inner coil and to absorb the greater volume of heat applied thereto.

References Cited in the file of this patent UNITED STATES PATENTS 219,311 Salisbury Sept. 2, 1879 1,334,560 Scott Mar. 23, 1920 1,975,104 Junkins Oct. 2, 1934 2,158,735 Vigneault May 16, 1939 2,548,081 Touloukian Apr. 10, 1951 2,615,434 Patterson Oct. 28, 1952 2,656,821 Ray Oct. 27, 1953 2,718,217 Walter Sept. 20, 1955 FOREIGN PATENTS 1,561 Great Britain of 1853 

